In order to produce a fine pattern on a substrate like a semiconductor wafer, flat panel display or the like in a technical field of fabricating a semiconductor device, plasma is generated to perform a variety of surface treatment processes including dry etching process, chemical vapor deposition process, sputtering and the like. In order to reduce cost and improve throughput, the size of a semiconductor wafer and that of a substrate for a flat panel display has shown a tendency of getting larger, for instance, over 300 mm in recent years. Accordingly, a device for generating plasma to process such a large wafer or substrate gets larger.
Widely used types of plasma generators include an inductively coupled plasma generator, a capacitively coupled plasma generator and the like. In addition, there has been proposed a method in which a magnetic field is applied to a general plasma generator.
Even if an inductively coupled generator is advantageous in obtaining high density plasma, it requires many additional elements for achieving a uniform density distribution. For example, a dielectric element having a central part thicker than the other parts, or a dome-shaped antenna, is used, which is, however, complex and difficult to be applied to an etching process of oxide.
The above-described inductively coupled plasma generator includes a chamber in which plasma is generated. The chamber includes a gas inlet opening for supplying reactant gas, a vacuum pump for keeping the internal part of the chamber in a vacuum state and a gas outlet opening for exhausting reactant gas after reaction. In addition, there is a chuck on which a specimen such as a wafer, glass substrate or the like will be placed in the chamber. An antenna connected with a high frequency power source is installed on the chamber. An insulating plate is installed between the antenna and the chamber for decreasing capacitive coupling characteristics, which helps transmission of energy from the high frequency power source to plasma through the inductive coupling.
The plasma generator thus constructed operates as follows. In other words, all the air filling in the internal part of the chamber is discharged out with a vacuum pump to get to a vacuum state at the first step. A reactant gas is infused for generating plasma through the gas inlet opening, and the chamber is kept at a necessary level of gas pressure. Then, the high frequency power is applied to the antenna device from the high frequency power source.
The conventional plasma generator is constructed with a spiral shaped antenna or a plurality of divided electrode type antennas. Therefore, with radio frequency (RF) power, a vertical magnetic field is formed along with changes of time at a plane horizontal to the antenna. The magnetic field that changes in time as such forms an inductive electric field at the internal part of the chamber. When electrons are heated and induced to an electric field to thereby generate plasma inductively coupled with the antenna. As described above, electrons are collided with neighboring neutral gas particles to generate ions and radicals and the like which will be used for plasma etching and deposition processes. In addition, if power is applied to the chuck from a separate high frequency power source, it is possible to adjust the energy of ions, which will be applied to the specimen.
A number of wires to form a spiral shaped antenna are connected in series, keeping flow of current constant in each wire. In this case, it is difficult to control distribution of inductive electric fields, and ions and electrons are lost at the internal wall of the chamber. Therefore, a high density of plasma is formed at the central part of the plasma, but a low density of plasma is formed at the part close to the internal wall of the chamber. As a result, it is extremely difficult to achieve uniformity in the density distribution of the plasma.
Furthermore, as all the wires of the antenna are connected in series, there may be a great voltage drop, which may increase the influence of a capacitive coupling characteristic with the plasma. Thus, the electrical efficiency of the antenna decreases and it is difficult to keep uniformity in the density distribution of plasma.
Next, in the antenna constructed with three separate electrodes respectively connected with three different phases of high frequency power sources, the density of plasma is generally high, but the density of plasma decreases at a part close to the center of the chamber. It is also difficult to ensure the uniformity in the density distribution of plasma, and it is more difficult to treat a large size of a specimen. In addition, application of separately operated power results in increase in cost because an independent impedance matching circuit should be used for separate electrodes to achieve an impedance matching state for efficient uses of power.
To overcome the above-described problems, the applicant of the present invention proposed an inductively coupled plasma generator in which an external antenna and an internal antenna are independently formed, in Korean Patent Application No. 2000-65696. In the proposed generator, a first inductive coil and a second inductive coil are formed at one end of each of the external and internal antennas, so that the first and second inductive coils establish mutual induction. Thus, if RF power is supplied to the external antenna, power having the same frequency as that supplied to the external antenna is supplied to the internal antenna having the second inductive coil according to the mutual induction of the first and second inductive coils. The power supplied to the internal antenna can be adjusted by controlling the crossing rate of the first and second inductive coils and by axially shifting a ferrite core.
The above-described plasma generator has a problem in that a plasma density distribution inside a chamber is not uniform due to the configuration of a loop antenna. In other words, when viewed from the cross-sectional view of the conventional loop antenna shown in FIG. 1, taken along the lines A–A′ and B–B′, a relatively high-density zone (Z) is formed at the central part of the antenna 1, and the powered end and ground end of the antenna 1 are relatively low-density zones. Plasma density distributions along the lines A–A′ and B–B′ are neither symmetrical nor uniform. As described above, a plasma density distribution is asymmetrical with respect to the rotating direction because a relatively high voltage is applied to a powered end of the antenna to cause ionic loss, resulting in a drop in plasma density. Also, since the flow of current at a disconnected portion of the loop antenna, that is, between the powered end and the ground end, is zero, no inductively electric field is generated thereat so that generation of plasma is reduced, resulting in a drop in plasma density.
The conventional antenna also has a problem in that dusty particles are produced in plasma due to a high voltage applied thereto, thereby lowering the yield of semiconductor devices.